A Boeing 747 can carry 48,445 gallons (183,380 liters) of fuel in a labyrinth of tanks so large that people can actually walk and crawl inside them. Can't believe it? Just watch.

The team from BBC's Engineering Giants did just that while going through the D-Check of a British Airways' Jumbo airliner. One of the presenters went with one of the technicians in charge of inspecting the gas tanks for leaks—from the inside.